The invention relates generally to magnetron sputtering. In particular, the invention relates to the configuration and placement of a rotatable magnetron.
A plasma sputter reactor typically includes a sputtering target, a water support pedestal which is arranged to face the consumable erosion surface of the sputtering target, and a magnetron which is arranged to face the back surface of the sputtering target. A magnetron creates a magnetic field adjacent to the erosion surface of the target to increase the plasma density and hence the sputtering rate. A working gas, such as argon, is fed into the vacuum chamber of the sputter reactor to generate a plasma near the sputtering target. Particles sputtered from the sputtering target reach the wafer to form a film.
The continuing development of miniaturized semiconductor devices has prompted a strong demand for full coverage at the bottom of inter-level connection holes, known as via or contact holes, having a high aspect ratio. In order to meet this demand, the present inventors have studied methods for improving the bottom coverage within the hole achievable by sputtering.
It is also important to improve the in-plane uniformity of the thickness of a film formed on a substrate by sputtering. For example, accompanying the development of large glass substrates for liquid-crystal and large semiconductor wafers, as exemplified in the transition from 200 mm to 300 mm wafers, there has been a great demand to further improve the in-plane uniformity of film thickness.
Accordingly, it is desired to provide a sputter reactor and a sputtering deposition method for improved bottom coverage.
It is also desired to provide a sputtering reactor and a sputtering deposition method for improved in-plane uniformity of film thickness.
In addition to the uniform sputter deposition, it is also desired to uniformly sputter the erosion surface of the target to maximize target utilization.
The invention includes a magnetron sputtering reactor and a method of sputtering in which a magnetron is positioned at the back of a target composed of a material to be sputtered. The magnetron is rotated about the center of the target to provide uniform sputtering and sputter deposition.
According to one aspect of the invention, the magnetron includes an outer magnet band of one polarity enclosing an inner magnet band of the opposite polarity. Preferably, the inner magnet band encloses an aperture free of permanently magnetized material, although an aperture-free inner band is preferred in some configurations. Each of the bands may be formed of a single magnet or of multiple magnets arranged in substantially parallel band shapes. A magnetic yoke may support the magnets of both bands and magnetically couple the bands of opposed polarity. In the case of a band being composed of multiple magnets, a magnetic pole face having a band shape may be positioned on the ends of the magnets opposite the yoke and magnetically couple the magnets of the same polarity, thereby bridging the region between the discrete magnets.
According to a second aspect of the invention, the magnetron is unbalanced and the total magnetic flux produced by the outer magnet band is greater, preferably by a factor of at least 1.5, than the total magnetic flux produced by the inner band. Thereby, the magnetic field may be projected toward substrate being sputter coated.
According to a third aspect of the invention, the magnetron is substantially confined to one side of the rotation shaft positioned at the center of the target and rotating the magnetron about the target center. Excursions of the magnetron to the other side are limited to small fractions of the target radius, for example, 15%. Preferably, the outer magnet band overlies the target center.
According to a fourth aspect of the invention, the curvature of the shape of the small-area magnetron is limited. Such shapes include circles and ovals having ratios of the minor axis to the major axis of at least 0.8. The oval""s major axis is preferably arranged along a target radius, but other orientations are possible. However, the invention may also be applied to other shapes of magnetrons, including triangles, arced triangles, and racetracks having parallel bands extending from near the target center to near the target periphery.
According to a fifth aspect of the invention, the magnetron includes nested pairs of magnet bands.
According to a sixth aspect of the invention, the magnetron may be formed of cylindrical magnets of one magnetic polarity arranged in an outer band having an oval or circular shape and cylindrical magnets of the other magnetic polarity arranged within the outer band. Preferably, the magnets in the outer bands have differing strengths, the stronger magnets being disposed closer to the target periphery.
The invention allows increased ionization of the sputtered atoms and provides magnetic guidance of the sputtered ions accelerated towards the substrate being sputtered coated. Thereby, deep hole filling is facilitated, and center-to-edge uniformity is improved.